1. Field of the Invention
The present invention relates to a color image forming apparatus, such as a color printer or a color copier, and more particularly, to a method and an apparatus to control the scanning velocity and the amount of light scanned in the color image forming apparatus.
2. Description of the Related Art
When the printing velocity in color image forming apparatuses, i.e., color laser printers, is varied so as to improve the deposition ability, the scanning velocity should also be varied according to the variation in the printing velocity. In this case, since the amount of light scanned increases if the scanning velocity is low, the amount of light scanned should be reduced. However, when the amount of light scanned cannot be reduced, there are problems in that toner is not well developed on a photosensitive body and background development occurs on printed paper. In order to prevent these problems, in a conventional method of controlling the amount of light scanned according to the scanning velocity, video data is pulse width modulated (PWM) when the printing velocity is varied, and the amount of light is controlled using a pulse width modulated (PWM) signal. However, the conventional method cannot finely vary the amount of light.
Further, a conventional color laser printer should include an additional oscillator (not shown), which generates a motor clock signal used to control a polygonal motor embedded in a laser scanning unit (LSU) and to adjust the scanning velocity, and thus printer manufacturing costs and volume increase. In this case, the additional oscillator only generates a motor clock signal having a fixed frequency, and thus the frequency of the motor clock signal cannot be varied according to the variation in the printing velocity.